The present invention generally relates to film formation technology used for forming a thin film on a substrate by a reaction of a source gas in a depressurized processing vessel, and more particularly to a thin film formation apparatus that produces a source gas from a source material of solid state or liquid state and supplies the produced source gas to a processing vessel. Further, the present invention relates to a thin film formation method that uses such a film formation apparatus.
A CVD (chemical vapor deposition) process is a film formation process that introduces a source gas into a processing vessel accommodating therein a substrate to be processed and deposits a desired thin film on the substrate by utilizing a chemical reaction taking place on the substrate surface or in gas phase.
In many cases, the source gas used with a CVD process is formed by vaporizing a volatile compound of the element constituting the thin film either in a solid state or in a liquid state. Generally, this is made by causing vaporization of a volatile compound held in a source vessel as a source material, by introducing a carrier gas, typically an inert gas, into the source vessel. Thereby, there is provided an open/close valve or inlet valve in a source gas supply line connecting the source material vessel and the processing vessel, and the inlet valve is controlled such that it is opened only when the source gas is to be introduced into the processing vessel.
Meanwhile, an ALD (Atomic Layer Deposition) process draws attention these days as an important film formation technology of semiconductor device production (Patent Reference 1, for example). Especially, film formation of a barrier metal film used for an interconnection structure of semiconductor devices or film formation of a high dielectric constant film typically used for a gate insulation film of MOSFET or a capacitor insulation film of capacitor, is thought as the field in which application of ALD process is highly effective.
In an ALD process, the foregoing conductor film or insulator film is formed on a substrate to be processed such as a semiconductor wafer one atomic layer by one atomic layer, and thus, two reaction gases are supplied to a processing vessel intermittently and alternately with a period of several seconds while interposing a purging step therebetween. Contrary to this, it should be noted that other conventional gas phase growth process such as a CVD process supplies a reaction gas to the processing vessel continuously. As a result of the chemical reaction of the reaction gases taking place intermittently, there is formed a layer of one atomic layer thickness or one molecular layer thickness in each one cycle of the gas supply sequence. Further, by repeating the gas supply sequence in plural times and by controlling the number of repetitions, it is possible with the ALD process to control the thickness of the thin film formed on the substrate arbitrarily.
With conventional ALD process, the ALD apparatus has been constructed such that a part of the source gas supply line located at the upstream side of an inlet valve is connected to an evacuation part such as a vacuum pump, or the like, by way of an evacuation bypass line, for enabling the desired intermittent supply for the reaction gas of the major constituent element of the thin film, and hence the source gas, to the processing vessel. Thereby, an open/close valve or an evacuation valve provided in the evacuation bypass line for evacuation is controlled in a complementary mode or reverse mode with regard to the operation of the inlet valve. Thus, in the interval of introducing the source gas to the processing vessel, the inlet valve is opened and evacuation valve is closed. Further, during the interval in which the source gas is not introduced to the processing vessel, the inlet valve is closed and the evacuation valve is opened such that the source gas produced in the source vessel is discarded to an evacuation part through the evacuation bypass line.
(Patent Reference 1) Japanese Laid-Open Patent Application 6-089873 official gazette